The invention relates to a disc brake with an actuator, which acts on a brake application device for applying at least one brake pad in the direction of a brake disc, the brake application device having a brake-internal hydraulic arrangement and being configured, to have a self-energizing design.
Disc brakes with actuators, such as an electric motor actuator, which act on a brake application device, for example a rotary lever having pressure pieces arranged behind it, are known in a very wide range of embodiments. It is also known to configure the disc brakes in the self-energizing design, in order for it to be possible to give the electric motor smaller drive dimensions. DE 101 05 752 A1 and DE 103 24 424 A1 disclose examples of brakes of this type. The known concepts, however, cannot practically operate. There is, therefore, the requirement for new solution approaches.
The maximum required motor output for the electric brake application and the corresponding gear mechanisms for force transmission form a decisive cost factor. The coefficient of friction of the brake pad changes, above all, as a consequence of heating, which plays a particular role, for example, in disc brakes for trucks. The motor output which is required here is considerable and entails additional costs for the provision of the electrical supply.
A disc brake having a brake-internal hydraulic arrangement is known, for example, from U.S. Pat. No. 4,435,021 or DE 195 27 936 A1.
A further disc brake is known from DE 101 05 540 A1, in which an electric motor acts as an actuator on a brake-internal hydraulic arrangement via pistons. However, this disc brake can be controlled or regulated only with relative difficulty with regard to its self-energizing action.
The object of the present invention comprises the elimination of this problem.
The invention provides a disc brake with an actuator which acts on a brake application device for applying at least one brake pad in the direction of a brake disc. The brake application device has a brake-internal hydraulic arrangement and is configured in a self-energizing design. The brake pad is supported on the brake application device at a wedge angle, wherein the hydraulic arrangement has a working unit for switching over the wedge angle, at which the brake pad is supported on the brake application device.
Thus, in a self-energizing brake, the invention makes it possible always to achieve optimum force boosting of a self-energizing brake of this type in a simple way, since the inclination or wedge angle, at which the brake application device acts on the brake pad, is of adjustable configuration during the braking operation. This makes simple and effective wedge angle setting possible even during a braking operation.
The brake boosting effect according to the wedge feeding principle can be used by way of a working unit, which has a preferably hydraulic cylinder having a step piston, while at the same time any desired wedge angle adaptation in precision stages can take place at any time during a braking operation.
The invention therefore has a device for wedge angle setting, which is actuated hydraulically. The working unit for wedge angle adjusting could also be realized in a different way than by a piston, this embodiment being preferred.
Here, a parking brake function can also be integrated, which is based not on hydraulics but on purely mechanical components. The brake can be released again reliably with the aid of the self-energizing hydraulic cylinder, that is to say the working unit.
Wedge angle setting is known per se in self-energizing brakes from DE 1043 24 424 A1. However, a separate gear mechanism arrangement or a separate actuator is required there for the wedge angle setting, in addition to the actual brake application apparatus for applying the disc brake.
The brake-internal hydraulics permit an entire series of embodiments of disc brakes with an electric motor actuator. For example, the electric motor is used as a drive for a pump, which acts on the brake-internal hydraulics. Fluid lines to the brake are therefore no longer required. A cable is sufficient, for example with an energy supply line and a control line. Nevertheless, the advantages of the hydraulic design can therefore also be used in a brake which is driven primarily by the electric motor and is actuated via electrical signals.
Here, according to one development, the brake application device preferably has a lever unit with at least one or more levers, which affords structural and design advantages because the lever arrangement is particularly reliable and secure. According to the prior art, in contrast, self-energizing brakes have been configured as a rule with a wedge arrangement. This variant can be combined with the brake-internal hydraulics which are explained in the above text, but also with a different type of brake application apparatus without hydraulics.
The force transmission of this electrically driven self-energizing brake is preferably performed on a hydraulic basis by use of a brake fluid. Forces and travels can be converted in a simple manner with the aid of the hydraulic fluid.
As a result of the use of hydraulics, which is delimited spatially to the brake, the accumulation of water in the brake fluid can be prevented largely with the avoidance of flexible brake linings and expansion containers made from plastic, which increases the service life significantly.
In one preferred embodiment, the hydraulic cylinders are double-action, the working unit being connected hydraulically between their first pressure connections and the gear pump being connected hydraulically between their second pressure connections. A different application of the hydraulic cylinders can therefore be achieved by means of this arrangement and by means of the working unit, which even affords the advantage that this application is coupled with wedge angle setting, which can also be set during the braking operation.
In one embodiment, the operative connection of the hydraulic cylinders is configured with supporting levers, which results in an advantageous simple construction with small dimensions. Here, it is advantageous in an alternative embodiment that the supporting levers are operatively connected to the hydraulic cylinders via power boosting levers.
A further embodiment is particularly advantageous, in which the supporting levers are operatively connected by way of, in each case, one end to the brake linings via a tilting apparatus, the tilting apparatus being connected in an articulated manner to the supporting levers and the brake lining. This advantageously makes the function of a mechanical parking brake possible.
It is advantageous in another embodiment that the brake lining is provided with a parallel guide device.
There is provision according to one preferred embodiment for levers, in particular supporting levers, to be provided which have a V-shaped design. The supporting levers preferably are mounted pivotably in each case by way of one end on the brake lining and in each case by way of two ends on the adjusting lever, which makes it possible to use this apparatus for forward and reverse traveling in a vehicle. An inverted arrangement is likewise contemplated.
Moreover, it is advantageous here that, in the direction of the ends which are mounted in the brake pad, the supporting levers are of widened configuration in the direction of the pivoting axis of the ends, which ensures advantageously uniform brake pad guidance and wear in the transverse direction. An inverted arrangement with the wider ends toward the brake pad is also contemplated.
There is provision according to a further preferred embodiment for the adjusting lever to be mounted pivotably on the counterbearing in the region of the bearing points of the in each case, two ends of the supporting levers on its side which lies opposite the bearing points, the pivoting axes of the bearing points extending parallel to the pivoting axes of the bearing points of the supporting lever and being arranged in the transverse direction of the supporting levers offset with respect to the pivoting axes of the bearing points of the supporting levers. The advantage which results from this consists in the fact that this apparatus additionally makes the function of a mechanical parking brake realizable. To this end, it is expedient that the gear pump is configured such that it can be connected hydraulically to the hydraulic cylinder for the function of the parking brake, application and release of the parking brake taking place electrohydraulically but fixing being mechanical.
In a further embodiment, a wedge-like wear tracking device is provided between the adjusting lever and its counterbearing, a spring being provided for restoring the brake pad and for holding together the brake pad, the supporting lever and the adjusting lever, which makes a simple space saving design possible.
It is preferred that the working unit has a step piston having a low pressure connection, a high pressure connection and a supply pressure connection, the step piston having a reduction in its piston diameters, which reduction is arranged in a step-like manner, and the area contents of the individual steps of the working unit preferably being configured in a ratio of 2:1. Furthermore, there is provision here for it to be possible for the individual steps of the working unit to be connected to the supply pressure connection or the high pressure connection. This results in the advantage, when this working unit is used according to the invention, that the step piston which can be switched over can perform an adaptation which acts as switchover of the wedge angle at any instant during a braking operation. In the case of three steps which can be combined, eight different angular settings result, for example.
There is provision in a further embodiment for the apparatus to have pressure sensors for detecting the brake application force and braking force, and the brake lining wear.
Moreover, the apparatus is equipped with a supply pressure circuit having an expansion vessel and a shutoff valve, the components being situated on the brake and making an advantageously simple hydraulic construction possible.
Finally, it is advantageous if the disc brake has a control device, in particular a control unit which is either arranged directly on the brake or is designed as another control device of a superordinate control system of the vehicle, which is designed to control or regulate at least the wedge angle setting during a braking operation, the regulation preferably taking place as a function of the brake application force and the currently set wedge angle.
The invention provides an advantageous disc brake with an actuator which acts on a brake application device for applying at least one brake pad in the direction of a brake disc, the brake application device having a lever arrangement with at least one or more levers, the at least one lever being of a V-shaped configuration. A simple and uncomplicated lever design is provided in this way.
Identical designations are used for parts having an identical or similar function.